Mechanism for adjusting the exposed surface area and position of an electrode along a lead body

ABSTRACT

An endocardial pacing and/or cardioversion/defibrillation lead having a plurality of electrodes and a mechanism for adjusting the exposed surface area of one or more electrode and/or the position and/or angular orientation of an electrode along a lead body. A fixed exposed, flexible, elongated commutator surface is provided extending along the lead body intermediate the proximal and distal lead body ends coupled by an electrical lead conductor extending to the proximal end of the lead body. A movable electrode assembly is provided that fits over and slides along the lead body, including the fixed commutator surface, that supports an exposed movable electrode on it. The movable electrode assembly includes at least one flexible, elongated, movable commutator surface within it that is electrically connected with the movable electrode. Electrical contact is established between the movable electrode and the lead connector end through contact of the fixed and movable commutator surfaces in a contact segment of contact area that varies with the relative movement of the movable contact surface with respect to the fixed contact surface. The position and exposed surface area of the movable electrode may be adjusted even further by use of a further electrode adjustable area outer insulating sheath positioned over the movable electrode assembly.

FIELD OF THE INVENTION

The present invention pertains to improvements in intracardiacelectrical stimulation and/or sensing leads, and particularly toendocardial pacing and/or cardioversion/defibrillation leads having aplurality of electrodes and a mechanism for adjusting the exposedsurface area and/or position of one or more electrode along the leadbody to orient it to a desired anatomical site for sensing and/orstimulation.

DESCRIPTION OF THE BACKGROUND ART

Early cardiac pacemakers provided unipolar or bipolar sensing and pacingof a single chamber of the heart, typically the right ventricle,utilizing a pace/sense lead bearing a single electrode or a pair ofelectrodes, respectively, in contact with the heart chamber. Morerecently, pacing and/or sensing of both the atria and the ventriclesusing a pair of pace/sense leads and/or electrodes (unipolar or bipolar)has become common. These techniques typically provide pacing and/orsensing in the right ventricle, using a right ventricular electrode orelectrode pair, and the right atrium, using a right atrial electrode orelectrode pair, and generally use separate atrial and ventricular pacingleads to locate the electrodes in the respective chambers. This approachis relatively convenient in both epicardial and endocardial approaches,unless there is difficulty in passing two endocardial leadstransvenously through the same blood vessels. In addition, it issometimes difficult to position the atrial electrode(s) in goodelectrical contact with the atrial heart tissue.

Atrial and ventricular pacing leads typically employ active or passive,distal end fixation mechanisms, which may or may not constitute a distalelectrode, to maintain contact of the distal electrode with endocardialor myocardial tissue to ensure adequate stimulation or sensing. Forexample, such fixation mechanisms include active, retractable/extendablehelical coils adapted to be extended and screwed into the myocardium atthe desired site and passive, soft pliant tines (of the type describedin commonly assigned U.S. Pat. No. 3,901,502 to Citron) which engage ininterstices in the trabecular structure to urge a distal tip electrodeinto contact with the endocardium. The atrial pacing lead may be formedwith a J-shaped bend that allows the atrial electrode to be positionedin the atrial appendage and fixed there through use of the fixationmechanism.

Such pace/sense electrodes and distal tip fixation mechanisms are alsocurrently used in conjunction with large surface areacardioversion/defibrillation electrodes extending proximally along thelength of the lead sheath for either right atrial or ventricularplacement. Separate electrical conductors and connectors are employed toconnect the atrial cardioversion/defibrillation electrodes with animplantable pulse generator (IPG) connector terminal for applyingcardioversion/defibrillation shock energy to the respective heartchamber.

In these cases, the inter-electrode separation along the lead body andthe effective sizes of the electrodes are fixed and not variable in use.In a somewhat related field of cardiomyostimulation, however, it isknown to employ a muscle stimulation electrode having a variable lengthso that it may be surgically threaded through a muscle mass of a givensize as disclosed in commonly assigned U.S. Pat. No. 4,735,205 toChachques et al. Such electrodes, however, have no application inendocardial cardiac stimulation or sensing leads.

In order to avoid the difficulties and expense of implanting separateendocardial atrial and ventricular leads of the types described, it haslong been desired to provide a single atrial-ventricular (A-V) lead thatcan be used to position both the atrial and ventricular pace/senseelectrode(s) and, if warranted, a cardioversion/defibrillationelectrode, in desired locations in the right atrium and ventricle. Anumber of such "single pass" A-V pacing leads have been designed overthe years as described in commonly assigned U.S. Pat. No. 4,479,500 toSmits.

In one early approach, atrial and ventricular sense or pace/sensering-shaped electrodes are simply arranged along the outer sheath of thelead and separated apart by fixed inter-electrode distances. In thesedesigns, the proximal electrode(s) is expected to be positioned in theatrium when the distal tip electrode is fixed in the right ventricularapex as described, for example, in U.S. Pat. Nos. 3,903,897 to Woollons,4,365,369 to Goldreyer and 4,962,767 to Brownlee. Such leads aretypically intended for use in a system for sensing atrialdepolarizations or P-waves and both sensing ventricular depolarizationsor R-waves and applying ventricular pacing pulses to the ventricularapex.

Because internal heart anatomy varies among individuals, it is difficultto obtain a suitable location of the atrial electrode(s) in a positionwhere they will either sense atrial depolarizations or stimulate theatria properly. Consequently, a number of single-pass A-V leads havebeen designed having atrial and ventricular electrodes which areadjustable relative to one another along the length of a composite leadbody. Several designs encase both atrial and ventricular conductors in acommon outer sheath with either the atrial or the ventricular conductorwithin its own sheath and slideably mounted within a lumen of the outersheath, allowing axial adjustment of the relative positions of theelectrodes.

For example, an early single pass A-V lead is taught in U.S. Pat. No.3,865,118 to Bures, wherein a ventricular lead sheath is slideablymounted within a lumen extending the length of the atrial lead sheathand extends out the distal end thereof. Electrodes are attached to thedistal portions of the atrial and ventricular lead sheaths, andelectrical connectors are attached to the proximal ends of thesesheaths. Coaxial, atrial and ventricular, coiled wire conductors extendthrough the atrial and ventricular sheaths to the electrical connectorsat the proximal ends thereof. Adjustment of the ventricular lead andelectrode relative to the atrial electrode therefore results incorresponding adjustment of the axial separation of the ventricularconnector relative to the atrial connector. This results in a leadconnector that is not compatible with IPG connector elements that are infixed separation from one another, requiring a special adapter ormodification of the lead connector end.

Another early single pass atrial ventricular lead is taught by Sabel inU.S. Pat. No. 3,949,757. In this lead, the atrial lead sheath isslideably mounted within a lumen of the ventricular lead sheath. As withthe Bures lead, adjustment of the relative positions of the atrial andventricular electrodes changes the relative positions of the electricalconnectors, with the disadvantages discussed above.

More recent single pass A-V leads that overcome some of the problems ofthe Bures and Sabel leads are disclosed in commonly assigned U.S. Pat.Nos. 4,289,144 to Gilman and 4,393,883 to Smyth et al. In these A-Vleads, the ventricular sheath is slideably mounted within an outeratrial lead sheath. A bifurcated connector assembly with two connectorsheaths is mounted to the proximal end of the lead body. The atrialelectrode is electrically connected by a fixed coiled wire conductorextending the length of the outer atrial lead sheath to one connectorsheath. The proximal end of the ventricular lead sheath slideablyextends through the lumen of the atrial coiled wire conductor andthrough a lumen of the other connector sheath. The distal end of theventricular lead sheath extends through a side opening in the outeratrial lead sheath at a point proximal to an atrial lead sheathextension, which may have a J-shape. After the electrode separation isadjusted to the patient's heart, the protruding ventricular lead sheathand the ventricular conductor within it are trimmed. An electricalconnector pin is attached to the remaining proximal end of theconductor, a time consuming procedure. After attachment, furtheradjustment of the lead is precluded, as the ventricular sheath andconductor are then fixed.

A further problem common to several single pass A-V leads is that ofsealing the lead at the exit points of the inner lead sheath from thelumens in the outer atrial lead sheath or the proximal connector sheath.In the Smyth and Gilman leads, where a coiled wire conductor is exposedto the lumen of the outer atrial lead sheath that the ventricular leadsheath extends through, a fluid path from that lumen to the exterior ofthe lead raises the risk of current leakage.

In the '500 patent, the Smits lead is provided with an outer lead sheathhaving an adjustment means for altering the length of the sheath, suchas a circumferentially pleated sheath segment or slideably overlappingsheath segments. A first conductor mounted within the outer lead sheathhas means for allowing variation of its length, such as a large diametercoiled segment having increased axial flexibility. The outer sheath isslideably mounted around the inner sheath with the inner sheathprotruding therefrom. The inner lead sheath is fixed relative to theproximal end of the outer lead sheath so that variation in the length ofthe outer lead sheath alters the relationship of electrodes attached tothe distal ends of the inner and outer lead sheaths. A connectorassembly is attached to the proximal end of the outer lead sheath. Theouter sheath may be fixed relative to the inner sheath by engageableprojections and indentations on the inner and outer sheaths or by asuture. The Smits lead offers a number of advantages as stated in the'500 patent, but the advantages are offset by a complex manufacture ofthe lead body.

These prior art references are primarily directed to attaining a singlepass A-V lead wherein at least sensing of P-waves is assured by properlocation of the atrial sense electrode(s) in the atrium when theventricular lead distal end pace/sense electrode is lodged in the rightventricular apex. In the field of implantable cardioversion/defibrillation systems, a number of endocardial leads have been proposedor developed for providing atrial or ventricularcardioversion/defibrillation shocks along with sensing of atrialelectrical signals as shown, for example, in commonly assigned U.S. Pat.Nos. 4,932,407 to Williams. The Williams leads include a coronary sinus(CS) cardioversion/defibrillation lead having an elongatedcardioversion/defibrillation electrode that is intended to be placedinto the ostium leading into the CS and blood vessels branchingtherefrom and more proximally located atrial pace/sense electrode(s)intended to be remain in or near the right atrium for sensing P-waves.The inter-electrode separation between the cardioversion/defibrillationelectrode and the atrial pace/sense electrodes is fixed.

In a somewhat related area, interest has existed for many years inachieving electrode positioning for electrical stimulation of specificsurfaces of the right atrium or atrial vessel openings adjacent toautonomic nerves or adjacent specific regions of current pathways for avariety of reasons. For example, research has shown that it may bedesirable to stimulate parasympathetic nerves in the sino-atrial (S-A)region of the right atrium that influence the atrial heart rate. Incommonly assigned U.S. Pat. No. 5,403,356 to Hill et al. (incorporatedherein by reference), the stimulation of the triangle of Koch and/or anarea of prolonged effective refractory period elsewhere in the atriumfor prevention of atrial tachyarrhythmias is also disclosed. Byelectrophysiological mapping techniques, it is possible to locateoptimum sites for electrical stimulation of the atrium. However, it isdifficult to place proximal electrodes of permanent endocardial atrialor ventricular or CS leads of the types described above, having fixedinter-electrode spacing, in proximity to these sites due to variationsin their locations, the sizes of the heart chambers, the extent to whichthe cardioversion/defibrillation electrode is extended into the CS, etc.

In all of these cases, it remains desirable to provide at least onerelatively movable electrode for achieving a variable inter-electrodeseparation from a fixed pace/sense electrode(s) or attachment site sothat the movable electrode may be placed optimally and be stabilized inthe optimal position while avoiding the problems attendant withconnection the proximal end of the lead to the IPG connector terminals.It would also be desirable to have the ability to select the exposedsurface area of the electrode to enhance sensing characteristics oroptimize stimulation energy distribution.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide asimple and flexible implantable endocardial lead providing variablepositioning of at least one electrode along the distal segment of thelead sheath.

It is a further object of the present invention to provide a simple andflexible implantable endocardial lead providing variable separationbetween a least two spaced apart electrodes along the lead sheath.

It is yet a further object of the present invention to provide forvariable electrode surface area of the variably positionable electrode.

These and other objects of the invention are realized in an elongatedimplantable lead of any of the types described above wherein a fixedexposed, flexible, elongated commutator surface is provided extendingalong the lead body intermediate the proximal and distal lead body endscoupled by an electrical lead conductor extending to the proximal end ofthe lead body. A movable electrode assembly is provided that fits overand slides along the lead body, including the predetermined segment,that supports an exposed movable electrode on it. The movable electrodeassembly includes at least one flexible, elongated, movable commutatorsurface within it that is electrically connected with the movableelectrode. Electrical contact is established between the movableelectrode and the lead connector end through contact of the fixed andmovable commutator surfaces in a contact segment of contact area thatvaries with the relative movement of the movable contact surface withrespect to the fixed contact surface.

The fixed commutator surface is located at a nominal distance from thedistal end of the lead body and a minimum contact segment between thefixed and movable commutator surfaces is defined to maintain an adequateelectrical connection. A range of movement of the movable electrodeassembly, and the movable electrode, between a maximum or proximaldistance and a minimum or distal distance is thereby defined by therelative lengths of the fixed and movable commutator surfaces and theminimum contact segment.

Preferably, the lead body is tubular, the fixed commutator surface isformed of a length of coiled wire wound about the tubular lead body, andthe movable commutator surface is formed of conductor wire wound into acoil inside the tubular shaped movable electrode assembly so that theoverlapping fixed and movable commutator surfaces are flexible and donot unduly stiffen the lead body. The exposed movable electrode is alsopreferably formed of a length of coiled wire and may constitute part ofthe coiled wire forming the movable commutator surface. The movablecommutator surface may extend proximally and/or distally of the exposedmovable electrode. The coiled wire winding diameter of the exposedmovable electrode may be greater than the coiled wire winding diameterof the movable commutator surface(s), or the diameters may be the same.

Insulating sheaths formed as part of the movable electrode assemblyextend proximally and distally from the exposed movable electrode andmovable commutator surface(s) sufficiently to cover and electricallyinsulate all of the fixed commutator surface at the extreme proximal anddistal positions of the movable electrode.

In a second aspect of the invention, the position of the exposed movableelectrode may be adjusted even further by use of a further electrodeadjustable area sheath positioned over the movable electrode assembly.The exposed surface area of the movable electrode is also varied by useof the adjustable area sheath. In this case, the exposed movableelectrode may be elongated since the final exposed electrode positionand surface area is determined by the further electrode adjustable areasheath.

The adjustable sheath may be a solid tubular sheath of a predeterminedlength exceeding the length of the exposed movable electrode, in whichcase a proximal or distal end band thereof may be selected as theexposed electrode surface area by relative distal or proximal,respectively, adjustment of the adjustable sheath. Alternatively, theadjustable sheath may have one or more window formed therein so that thewindow(s) may be selectively positioned along the length and around thecircumference of the exposed movable electrode surface. In this case,the exposed electrode surface may be oriented to a desired location orto direct stimulation current in a particular direction to stimulate oneof the sites identified herein.

The movable electrode of the present invention may be implemented into awide variety of leads including the intracardiac leads described above,to allow for positioning of the movable electrode in a desired locationfor sensing nerve and cardiac electrical signals and for deliveringelectrical stimulation at a precise location for stimulating nerves orheart tissue. A conventional lead connector end may be employed, and themovable electrode assembly does not unduly increase the outer diameterof the lead body or complicate the implantation procedure.

Advantageously, the movable electrode may be positioned along the leadbody to a specific site while taking variations in individual anatomyinto account. The movable electrode may be selected in surface area,distance along the length of the lead body and, in certain embodiments,angular orientation for stimulating cardiac tissue or nerves or sensingnerve or cardiac electrical signals for pacing, sensing,cardioversion/defibrillation or nerve stimulation applications. Theadjustment of the surface area of the exposed movable electrode inaccordance with the second aspect allows for control of electricalstimulation current density at the desired location.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages, and features of the presentinvention will become evident from the following detailed description ofexemplary preferred embodiments thereof in view of the followingdrawings wherein the same or like components are identified by the samedrawing numbers or indicia, and wherein:

FIG. 1 is a plan view of an endocardial lead incorporating the presentinvention in which a variable position electrode assembly and variablearea sheath are employed to define a location and size of an electrodeproximal to the distal end of the lead;

FIGS. 2-4 are each a side cross-section view of a first variation of theconstruction of a variable position electrode assembly of FIG. 1 anddepicting a range of movable electrode locations;

FIGS. 5 and 6 are each a side cross-section view of a second variationof the construction of the variable position electrode assembly of FIG.1;

FIGS. 7 and 8 are each a side cross-section view of the variableposition electrode assembly of FIG. 1 together with a variable areasheath for adjusting the exposed movable electrode surface area depictedin proximal and distal locations in accordance with a second aspect ofthe invention;

FIG. 9 is a partial cross-section view of the variable positionelectrode assembly of FIG. 1 together with a variable electrode positionand angular orientation determining sheath for locating and orienting asheath window over the movable electrode surface in accordance with avariation of the second aspect of the invention;

FIG. 10 is a schematic illustration of an application of the presentinvention in a single pass, endocardial, A-V pacing lead positioned inthe heart wherein the movable electrode assembly may be positioned inthe atrium or superior vena cava (SVC) for sensing or stimulating nervesor atrial heart tissue;

FIG. 11 is a schematic illustration of an application of the presentinvention in an atrial J-shaped endocardial lead positioned in the heartfor effecting either nerve or heart tissue stimulation and sensing at aselected location of the movable electrode assembly with respect tonerves or atrial heart tissue;

FIG. 12 is a schematic illustration of an application of the presentinvention in a single pass A-V lead having a movable electrode assemblyfor locating a sense or stimulation electrode in the right atrium orsuperior vena cava proximally to a ventricularcardioversion/defibrillation electrode positioned in the right ventricleof the heart;

FIG. 13 is a schematic illustration of an application of the presentinvention in a single pass A-V lead having a movable electrode assemblyfor locating a sense or stimulation electrode in the right atrium or SVCproximally to an elongated cardioversion/defibrillation electrodepositioned in the coronary sinus of the heart;

FIG. 14 is a schematic illustration of an application of the presentinvention in a single pass A-V lead having a movable electrode assemblyfor locating an elongated cardioversion/defibrillation electrode in theright atrium and/or SVC proximally to a ventricularcardioversion/defibrillation electrode positioned in the right ventricleof the heart; and

FIG. 15 is a schematic illustration of an application of the presentinvention in a single pass, endocardial, coronary sinus pacing leadwherein the movable electrode assembly may be positioned in the coronarysinus or in the atrium for sensing or stimulating atrial heart tissueproximally to a distal ventricular pace/sense electrode positioned deepin the coronary sinus or a tributary thereto adjacent the ventricles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in a number of preferred embodimentshaving a number of intended uses as set forth in the precedingdescription, and other uses will become apparent to those of skill inthe art. In the preferred embodiments, a single variable positionelectrode is described that may be positioned within a range of possiblelocations along a segment of the length of an endocardial lead outersheath in relation to the distal end thereof. It will be understood thatthe lead may include at least one further variable position electrode sothat the inter-electrode spacing and location of the electrodes alongthe lead sheath may be optimized for a particular application. Incertain applications, the distal end of the lead sheath may include apace/sense electrode(s) or an elongated cardioversion/defibrillationelectrode and/or a fixation mechanism for stabilizing the lead.

The embodiments of the present invention are further described as havingcoaxial lead conductors employing proximal, variable position,ring-shaped electrodes and in-line connector assemblies and providedwith an innermost lumen for receiving a stiffening stylet as isconventional and widely employed in the art. It will be understood thatthe lead conductor configuration may alternatively take any of the knownforms, including separate, single or multi-filar coiled wire or straightconductors located in separate lead body lumens or multi-filar,separately insulated, parallel wound, coiled wire conductors of the typedescribed in commonly assigned U.S. Pat. No. 4,944,088 to Doan et al.and in Canadian Pat. No. 1,146,228 to Upton, incorporated herein byreference in their entireties. Finally, the present invention isdescribed in its preferred embodiments as having unipolar or bipolaratrial and ventricular electrodes. However, configurations employingmulti-polar electrodes are within the intended scope of the invention. Awide variety of configurations employing different combinations of theseelements are within the intended scope of the invention.

In FIG. 1, a plan view of a generic, single pass, lead embodying thefirst aspect of the present invention is depicted. In this embodiment,it will be assumed for convenience of illustration and description thatthe lead body is formed using co-axial coiled wire lead fabricationtechniques that are well known in the art having an inner lumen forreceiving an inner, coiled wire, lead conductor and at least one outer,co-axial lumen surrounding the inner lumen for receiving an outerelongated, coiled wire, lead conductor. A pace/sense electrode 10 and apliant tine, passive fixation mechanism 12, for example, are located atthe distal end of a distal extension of an inner lead sheath 20 thatextends from a fixed commutator surface (described below) forming partof the lead body at the distal terminus of an elongated, outer leadsheath 14 and encased by a variable position, movable electrode assembly34. The elongated outer insulating lead sheath 14 extends from aproximal, in-line, connector assembly 16 to the fixed commutatorsurface. The inner lead sheath 20 extends from the fixed commutatorsurface of the movable electrode assembly 34 to distal pace/senseelectrode 10. A suture sheath 17 is mounted around insulating sheath 14to be moved along it and fixed at a desired location to anchor the outerlead sheath 14 at the point of venous entry in a manner well known inthe art. Connector assembly 16 includes a connector pin 24 and aring-shaped connector element 22, separated by an insulating sheath 26.and a distally extending reinforcing sheath 28. The connector assembly16 is provided with resilient sealing rings 30 and 32, which seal theconnector assembly 16 when it is inserted into an elongated receptaclein a connector block mounted to an IPG (not shown).

In accordance with a first aspect of the present invention, the variableposition electrode assembly 34 supports an exposed ring-shaped, orpartial ring-shaped segment, movable electrode 18. The movable electrode18 is supported between proximal and distal movable insulating sheaths36 and 38 of the assembly 34 adapted to be positioned over the fixedcommutator surface of the lead body and the exterior surface of outerand inner lead sheaths 14 and 20, respectively. The variable positionelectrode assembly 34 also includes an inner commutator surface thatcontacts the exterior commutator surface of lead sheath 14 in aselectable area of contact as described in detail with reference toFIGS. 2-9. In accordance with a second aspect of the invention, theexposed surface area of movable electrode 18 may preferably be adjustedthrough the use of a further outer insulating electrode area sheath asdescribed below in reference to FIGS. 7-9.

The connector pin 24 is electrically and mechanically connected to thedistal tip electrode 10 by an elongated inner coiled wire electricalconductor (or a conductor of one of the other conductor types listedabove) extending within the inner lead sheath 20 for the full length ofthe lead. Similarly, the connector ring element 22 is electrically andmechanically connected by an elongated outer coiled wire conductor (orone of the other conductor types listed above) located within outersheath 14 which is electrically connected to the movable electrode 18through the commutator mechanism described in reference to FIGS. 2-6.

Connector pin 24, ring member 22, variable electrode 18, and distal tipelectrode 10 are preferably fabricated using inert conductive metalssuch as platinum, Elgiloy® alloy, MP35N or stainless steel. Insulatingsheaths 26 and 28 are preferably fabricated of silicone rubber, andouter insulating sheath 14, inner insulating sheath 20 and movableproximal and distal, movable insulating sheaths 36 and 38 are preferablyfabricated of polyurethane or silicone rubber.

In FIG. 1, the distal tip of the lead constitutes a reference point DTwith respect to a range R of possible locations of the ring electrode 18along outer lead sheath 14 about a nominal location N and betweenminimum and maximum distances D_(min) and D_(max),. The range R and thedistance D from the distal tip DT to the nominal position N may beselected for the particular applications depicted in FIGS. 10-15 andother applications that may become known to those of skill in the art.

FIG. 2 shows a side sectional view of a first embodiment of the movableelectrode assembly 34 without an outer sheath for adjusting the exposedsurface area of the movable electrode 18. For simplicity ofillustration, the lead body 40 is shown as solid having a straight innerconductor 42 extending between the distal tip electrode 10 and theproximal connector pin 24 (which may constitute one manner ofconstructing the lead body 40). It will be understood that the innerconductor 42 may be a coiled wire conductor coiled to define an innerlumen for receiving a stiffening stylet, as is conventional in the art.Similarly, the outer conductor 44 is depicted as a solid, whereas inpractice, it is preferably constructed as a coiled wire conductor thatmay co-axially surround the inner conductor 42 and be insulatedtherefrom by the inner lead sheath 20 extending distally to theconnector assembly 16 in a manner well known in the art. Other conductortypes of the types listed above may be alternatively employed to performthe functions of the inner and outer conductors 42 and 44.

The movable electrode assembly 34 further preferably comprises aflexible commutator mechanism including an elongated, fixed commutatorsurface 48 electrically connected to the distal end of the outerconductor 44. The fixed commutator surface 48 is exposed at the terminusof outer lead sheath 14 so that it may make electrical contact with anelongated movable commutator surface 50 within the proximally extending,movable insulating sheath 36 in an overlapping, band-shaped, contactsegment. Preferably, the fixed commutator surface 48 is formed of anelongated coiled wire conductor that is closely wound over an enlargeddiameter section of the inner lead sheath 20 (or a flexible spacersheath over inner lead sheath 20). Alternatively, the winding may bespaced so that the coil turns are partially embedded in inner leadsheath 20 (or such a flexible sheath) leaving at least the outermostportion of the coils exposed in a manner known in the art for thefabrication of exposed, coil wire turn electrodes.

In the preferred embodiment wherein the outer conductor 44 is formed ofa single or multi-filar coiled wire conductor, the fixed commutatorsurface 48 may be formed of a number of turns of the coiled wire outerconductor 44 at the distal end thereof that are expanded in diameter toapproximate that of the outer lead sheath 14. Where the outer conductor44 is formed of a straight wire or in another manner, it may beelectrically and mechanically connected to the coiled wire conductor ofthe fixed commutator surface 48 by welding or the like in a manner wellknown in the art.

Similarly, the movable commutator surface 50 is preferably formed of alength of coiled wire conductor having closely wound turns or spacewound turns insulated by or partially embedded within the proximallyextending, movable insulating sheath 36. The movable electrode 18 ispreferably formed of a number of turns of the same coiled wire conductorextending proximally or distally from the coiled wire turns forming themovable commutator surface 50 that are expanded in diameter to fit overdistal insulating sheath 38. Again, the movable electrode 18 may beformed of closely wound or space wound turns of the coiled wireconductor in a manner well known in the art. Alternatively, the movableelectrode 18 is formed of a solid conductive ring that is electricallyand mechanically connected to the movable commutator surface 50 throughcrimping and welding techniques well known in the art. In that case, theconductive ring movable electrode 18 may be attached directly over turnsof the movable commutator surface 50, rather than offset distally orproximally as shown.

For convenience of illustration, the coiled wire turns of the fixedcommutator surface 48 are depicted as a conductive tubular element. Itwill be understood that the fixed and movable commutator surfaces 48 and50 are preferably both formed of coiled wire turns so that the lead body40 remains flexible over their lengths. The coiled wires turns formingthe fixed and movable commutator surfaces may be partially embedded ininsulation sheathes. As a result of using coiled wire conductors, thelead body 40 may bend in the region of the movable electrode assembly 34and make intimate contact with the endocardial wall or a cardiac vesselwall in a desired location and is not subjected to stresses that wouldarise if it were not flexible in that region.

Alternatively, the fixed commutator surface 48 may be formed of a lengthor parallel lengths of straight wire conductor embedded in the outersheath 20 and electrically connected to the coiled wire outer conductor44 or to a straight wire outer conductor(s) 44. The movable commutatorsurface 50 may alternatively take the form of discrete conductive bandsor segments bearing against the straight wire conductor, fixedcommutator surface 48.

The movable electrode assembly 34 has an inner diameter that snugly fitsover the outer diameter of the outer sheath 14, the exposed coilsurfaces of the fixed commutator surface 48, and the distal section ofthe inner lead sheath 20. The inner and outer diameter dimensions areselected to provide good electrical contact between the movablecommutator surface 50 and the fixed commutator surface 48 while stillallowing relative movement within the range R. The exposed portions ofthe coiled wires of the fixed and movable commutator surfaces 48 and 50making sliding and electrical contact with one another in the contactsegment may be shaped as spiral bands or as flattened outer or innerturn surfaces to optimize electrical contact and the ability to move themovable electrode assembly 34. A lubricant, e.g. silicone oil, may beused to allow relative movement while providing an interference fit ofthe inner and outer diameters of the movable and fixed commutatorsurfaces 50 and 48.

The lengths of the proximally and distally extending, movable insulatingsheaths 36 and 38 may vary from those shown in FIG. 2. The lengths areselected to maximize coverage and insulation of the fixed commutatorsurface 48, other than the contact segment, at extreme proximal anddistal positions of the movable electrode assembly 34 within the rangeR. The range R is defined by the relative lengths of the fixed andmovable commutator surfaces 48 and 50. Only limited lengths of eachcommutator surface 48 and 50 need to overlap in the contact segment tomake adequate electrical contact. Because the commutator surfaces 48 and50 are formed of coiled wire turns, it is likely that electrical contactmay be provided at a large number of contact points along theband-shaped contact segment. A large surface area contact segment is notnecessary for sensing electrical signals or for low energy stimulationof the heart chamber or autonomic nerves or the like.

However, it is necessary to stabilize the area of the contact segmentfrom relative movement due to the beating action of the heart or patientexercise in order to minimize electrical noise that may result from suchrelative movement. Consequently, in a first variation as illustrated,proximal and distal suture grooves 52 and 54 are provided to receivesutures to tie down the movable electrode assembly when an optimumdistance D is selected for a given location in a given patient. Othersuture grooves may be provided along a particularly lengthy movableelectrode assembly 34. The sutures stabilize the area of contact tominimize electrical noise, seal the contact surfaces from ingress ofbody fluids, and otherwise maintain the distance D. In order toelectrically insulate and preferably avoid fluid ingress into thejunction of the fixed and movable commutator surfaces 48 and 50, atleast a proximal section of the inner lead sheath extending from thedistal terminus of the fixed commutator surface 48 is preferablyenlarged in diameter as depicted or encased in a further sheathproviding an outer diameter consistent with that of outer lead sheath 14and fixed commutator surface 48. For purposes of the present invention,the enlarged diameter section of the inner lead sheath 20 by eithermethod may be considered as a distal extension of the outer lead sheath14.

As described below in reference to FIG. 9, the proximally extending,movable insulating sheath 36 may extend proximally into proximity withthe proximal connector assembly 16 so that the movable electrode 18 itmay be adjusted by the physician after the lead 10 is positioned in theheart. In other words, the proximal end of the proximally extending,movable insulating sheath 36 can be grasped to move the elongated sheathproximally or distally with respect to the fixed commutator surface 48.

FIGS. 3 and 4 depict other relative displacements of the fixed andmovable commutator surfaces 48 and 50 of the movable electrode assembly34 within its adjustment range R illustrated in FIG. 1. In FIG. 2, themovable electrode 18 is positioned at the distal extreme of the range Ror a minimum distance D_(min) (FIG. 1), depending on a safe minimumlength of overlap of the fixed and movable commutator surfaces 48 and 50and the length of the proximally extending, movable insulating sheath36. In FIG. 4, the movable electrode 18 is positioned at the proximalextreme of the range R or the maximum distance D_(max), (FIG. 1)depending on the safe length of overlap of the fixed and movablecommutator surfaces 48 and 50 and the length of the distal movableinsulating sheath 38. In FIG. 3, the movable electrode 18 is positionedintermediate the minimum and maximum distances D_(min) and D_(max),.

The range R thus depends on the lengths of the fixed and movablecommutator surfaces 48 and 50, the lengths of the proximally anddistally extending movable insulating sheaths 36 and 38 and the minimumlength of overlap of the fixed and movable commutator surfaces 48 and50. The exterior surfaces of the outer lead sheath 14 and the distalextension of the inner lead sheath 20 may be marked with markersidentifying the minimum and maximum distances D_(min) and D_(max),.Alternatively, movement of the movable electrode assembly 34 beyond therange R may be physically inhibited by stops formed in the exteriorsurfaces of the outer lead sheath 14 and the distal extension of theinner lead sheath 20.

FIG. 5 depicts a variation of the first embodiment wherein the movableelectrode 18 is positioned between a proximal and distal movablecommutator surface sections 50' and 50". Again, the movable electrode 18and the proximal and distal movable commutator surface sections 50' and50" are preferably formed of an extension of the outer lead conductor 42formed as a coiled wire conductor having differing coil inner diametersto provide the commutator surface 50. This variation may be employedadvantageously to provide elongated cardioversion/defibrillation movableelectrodes 18. Alternatively, the movable electrode 18 may be formed ofa solid metal band 18' that is crimped and attached to the coiled wire,movable commutator surface 50 extending proximally and distally as shownin FIG. 6.

It should also be noted that the exposed electrode 18 may be effected aseither a band or ring shape, as depicted, or may be a patch or segmentof a band shape to provide the capability of angularly orienting themovable electrode 18 toward a desired anatomical feature as describedbelow. This limited electrode may be effected by the form of theproximally and distally extending, outer insulating sheathes 36 and 38and/or by the shape of the attached band 18'. It is possible to form themovable electrode 18 as simply an exposed band or segment or patch ofthe coiled wire conductor forming the movable commutator surface 50without the expanded diameter of movable electrode 18 as depicted inFIGS. 2-6 and 7-9. In this case, the movable electrode 18 is simply anexposed exterior portion of the movable commutator surface 50 in theregion of electrode 18' of FIG. 6, for example. The exposed segment orpatch shaped movable electrode 18 may be effected by simply forming theproximally and distally extending, movable insulating sheathes 36 and 38as a single insulating sheath with a window opening in it to define theangularly orientatable movable electrode 18. A particular angularorientation may be effected by rotation of the movable commutatorsurface 50 and attached movable electrode 18 over the fixed commutatorsurface 48.

The second embodiment of the invention contemplates the adjustment ofthe surface area of the movable electrode 18 or 18' with a furthermovable, tubular, adjustable area, insulating sheath 60 that may befitted over it and moved distally or proximally with respect to theposition of the electrode 18. In this embodiment, the movable, flexiblecoiled wire, electrode 18 and the associated fixed and movablecommutator surfaces 50 may be fairly lengthy to allow for a wideadjustment range R. Then, the adjustment may be further fine tuned byadjusting the location of window opening(s) or ends of the adjustablearea insulating sheath 60 and applying sutures to the suture grooves 62and 64 or otherwise fixing the adjustable area sheath 60 in place. FIG.7 shows a proximal location of such an adjustable area insulating sheath60 leaving a distal band-shaped section of the movable electrode 18exposed. Similarly, FIG. 8 shows a distal location of the adjustablearea insulating sheath 60 leaving a proximal band-shaped section of themovable electrode 18 exposed for either sensing cardiac signals orstimulating a particular location in a heart chamber or vessel. Theadjustable area insulating sheath 60 may be employed with any of theleads depicted in FIGS. 1-6 and equivalents thereto.

In the variation of this aspect of the invention depicted in FIG. 9, themovable or adjustable area insulating sheath 60 is provided with one ormore window opening 61. The adjustable area insulating sheath 60determines a variable electrode position and angular orientation forlocating and orienting the sheath window opening 61 over an electrodesurface 18" defined in size by the window opening 61 so that electricalstimulation current flows in a desired direction or sensing ofelectrical signals is from a desired direction. Although only a singleposition is depicted, it will be understood that the adjustable areainsulating sheath 60 may be positioned along the length of overlap ofthe commutator surfaces in the manner described above with respect toFIGS. 2-4 or 5 and 6. The adjustable area insulating sheath 60 may alsobe rotated about the movable electrode assembly to orient the windowopening to the desired angle. This variation is particularly useful inorienting the exposed electrode surface in an optimum direction alongthe length of the lead body within the range R for sensing orstimulating nerves or fat pad areas as described below.

In this aspect of the invention, it should be noted that it may bepossible to employ a continuous length of flexible conductor, e.g. alength of coiled wire conductor, as both the commutator surface and themovable electrode surface, wherein the length of coiled wire conductorhas a common coil winding diameter. For example, the full length of themovable commutator 50 depicted in the embodiment of FIG. 6 (without theband electrode 18') could be employed as the movable electrode that ispositionable to overlap with the elongated fixed commutator 48. Then,the exposed surface area of the movable electrode 18 would be governedby the positioning of the adjustable area insulating sheath 60.

Although a single movable electrode assembly 34 (and optionallyadjustable area insulating sheath 60) is described to this point, itwill be understood that a fixed ring electrode or a second movableelectrode assembly may be provided along the outer lead sheath 14 spacedproximally from the first movable electrode assembly 34 by simplyenlarging the lead body to accommodate the additional lead conductor andinsulating sheath in separate lumens or by employing the separatelyinsulated conductor wires wound together in the same lumen in the mannerdisclosed in the above-incorporated '088 patent.

In accordance with a further aspect of the present invention mentionedabove and illustrated in FIG. 9, for example, the proximally extending,movable insulating sheath 36 may extend a distance sufficient that itends adjacent to the proximal connector assembly 16 but spaced from it,exposing the proximal suture groove 52 when the lead is transvenouslyimplanted. The distal suture groove 54 may be eliminated, and the distalend of distally extending, movable insulating sheath 38 may tightly fitover the distal extension of inner lead sheath 20. In this manner, theinsulating sheath 36 and the movable electrode assembly 34 may bemanually manipulated by the surgeon when the electrodes on the lead arepositioned within the heart. In this embodiment, the movable electrodeassembly 34 may be adjusted in situ while observing the cardiacstructure and the movable electrodes through fluoroscopy or othervisualization techniques. The position of the adjustable electrodeassembly 34 may also be tested by delivering stimulation pulses and/ormonitoring electrical signals of the heart or nerves. After an optimumposition is attained, the suture may be tied about the proximal suturegroove 52 to hold the desired position.

Similarly, with respect to the second aspect of the invention describedabove with respect to FIGS. 7-9, the movable, adjustable area,insulating sheath 60 may also extend proximally so that it may bemanipulated by the surgeon in the same manner. Markers may be providedon it and on the underlying proximally extending, movable insulatingsheath 36 to guide the adjustment of the exposed surface area and/ororientation of the electrode 18.

Exemplary applications for endocardial leads of the type described abovehaving one or more movable electrode assembly 34 with and without theadjustable area sheath 60 area are depicted schematically in FIGS.10-15. In each case, it will be understood that the ideal implantationlocation may be visualized using fluoroscopy, since the movableelectrode assembly 34 is radiopaque, and that the lead may be withdrawnfor adjustment or adjusted manually in situ by manipulation from theproximal lead of the movable electrode 18 if it appears to be toosuperior or inferior to the desired location. Once a desired generallocation is confirmed, the adjustable area sheath 60 may be used to finetune the location and size of the exposed surface of the movableelectrode 18.

In FIG. 10, a single pass, A-V lead 70 is depicted having the form shownin FIG. 1 and one of the movable electrode configurations depicted inFIGS. 2-9 in relation to the heart 100. The lead 70 is shown with ascrew-in fixation electrode 10' holding the distal tip in the apex ofthe right ventricle 102. The distance D that the movable electrode 18 isadjusted to allows the electrode 18 to be positioned high in the rightatrium or the SVC 106 in the location suggested in the '767 patentadjacent to the S-A node to facilitate sensing of the atrial EGM,particularly the P-wave. A second fixed (or adjustable) electrode 118 isalso incorporated in the lead 70 of FIG. 10 for bipolar sensing orstimulation, but may be absent for unipolar sensing or stimulation.

FIG. 11 depicts an atrial J-shaped lead 80 also having first and secondmovable electrode assemblies 34 and 134 positioned along the lead outersheath in a desired location in the right atrium 104. The position ofthe movable electrodes 18, 118 may be adjusted to optimize detection ofatrial EGM signals emanating from near the S-A node or the fat pads inthe triangle of Koch as described in the above-incorporated '356 patentor other areas of the atrial wall or the SVC 106 that the lead outersheath 14 bears against to detect desired signals or apply electricalstimulation to.

In a further application, the electrodes 18, 118 in FIGS. 11 and 12 maybe positioned to facilitate delivery of electrical stimulation throughthe atrial wall or the SVC wall to autonomic nerves to influence sinusheart rate, the A-V interval, and blood pressure or the like. Forexample, vagal nerve stimulation may be effected through the atrial wallby an electrode 18 that is oriented in the manner described above withrespect to the variation of FIG. 9 towards the vagal nerves. The vagalstimulation may be delivered during an episode of atrial fibrillation ortachycardia in order to slow the ventricular heart rate response to theatrial heart rate.

The present invention may also be used in endocardial leads havingelongated cardioversion/defibrillation electrodes extending proximallyfrom the distal tip thereof toward the more proximally located movableelectrode(s) 18. FIG. 12 depicts a ventricularcardioversion/defibrillation lead 74 having acardioversion/defibrillation electrode 76 in such a location and themovable electrode assembly 34, located proximally thereto in the mannerof FIG. 10. FIG. 13 depicts a CS lead 84 extending into the ostiumopening 110 and having a cardioversion/defibrillation electrode 86 ofthe type shown in the above-referenced '407 patent located in the CS108. The proximally located, movable electrode assembly 34 can beadjusted in position to be located outside the ostium opening 110 and inan optimum location for sensing the P-wave and/or pacing the atrium.

FIG. 14 is a schematic illustration of an application of the presentinvention in a single pass, atrial and ventricularcardioversion/defibrillation lead 174 having a ventricularcardioversion/defibrillation electrode 176 located in the rightventricle 102 and a movable cardioversion/defibrillation electrodeassembly 34, located proximally thereto in the right atrium 104 and/orSVC 106. In this case, the movable electrode assembly 34 is an elongatedcoiled wire conductor, exposed movable electrode 18 adjustably locatedin the right atrium 104 and/or SVC 106 for deliveringcardioversion/defibrillation shocks between the atrial and ventricularcardioversion/defibrillation electrodes in a manner well known in theart. For atrial cardioversion/defibrillation alone, the ventricularcardioversion/defibrillation electrode 176 may be eliminated. In bothcases, the distal ventricular pace/sense electrode and fixationmechanism 10 may be retained.

FIG. 15 is a schematic illustration of an application of the presentinvention in a single pass, endocardial, coronary sinus pacing lead 184wherein the movable electrode assembly 34 may be positioned in thecoronary sinus 108 or in the atrium 104 for sensing or stimulatingatrial heart tissue proximally to a distal ventricular pace/senseelectrode 10" positioned deep in the coronary sinus or a tributarythereto adjacent the ventricle 102. Alternatively, the movable electrodeassembly 34 may be positioned to sense or stimulate nerves or the fatpad as described above.

Other applications will be apparent to those of skill in the art using asingle or multiple movable electrode assemblies 34. In a ventricularendocardial lead, the movable electrode assembly(s) 34, 134 andelectrode(s) 18, 118 could be positioned to be located in the rightventricle in order to sense conducted or ectopic R-waves superior to theventricular apex, for example.

Theoretically, it may be possible to extend the length of the fixedcommutator surface 48 along a length of the lead body that should besufficient to traverse the largest atrial, atrial-SVC, or ventricularheart chamber so that the movable electrode 18 may be positionedanywhere along the length. It will also be understood that an elongatedfixed commutator surface 48 may be periodically reduced in diameter andinsulated to provide periodic exposed commutator surface rings along thelength thereof. In such cases, the proximal and distal insulatingsheaths 36 and 38 may be provided in excessively long lengths andtrimmed to cover the exposed fixed commutator surface 48 or periodiccommutator surface rings that are not covered by the electrode 18 andmovable commutator surface 50 or 50', 50".

Although the above described endocardial leads have distal tip, screw-inelectrodes 10", it will be understood that the present invention neednot be used with leads having such distal tip electrodes. The distal tipmay simply include an active or passive fixation mechanism forstabilizing the lead in the heart so that the variable positionelectrode assembly(s) 34, 134 may be maintained at the desiredlocation(s).

Other modifications and equivalents to the preferred embodiments of thepresent invention will become apparent to those of skill in the art.Although the disclosed embodiments and variations relate to endocardialcardiac leads for stimulating cardiac tissue or nerves and/or sensingnerve impulses or the cardiac EGM at selected locations in heartchambers or associated vessels, it will be understood that theprinciples and teachings of the present invention may be applicable toother leads for sensing electrical signals from or stimulating otherorgans or tissue of the body. Therefore, the disclosed embodiments andvariations should be considered as exemplary and not limiting as to thescope of the following claims.

I claim:
 1. An elongated implantable lead having a proximal lead end anda distal lead end comprising:an elongated lead body extending betweensaid proximal lead end and said distal lead end; a connector assemblylocated at the proximal end of said lead body; a first electricalconductor having a proximal conductor end coupled with said connectorassembly and extending through a proximal portion of said lead body to adistal conductor end; an elongated outer lead sheath extending betweensaid proximal and distal conductor ends for insulating said firstelectrical conductor through its length from body fluids and tissue;means for providing an elongated, flexible, fixed commutator surfaceexposed to body fluids and tissue extending along said lead body; meansfor coupling said elongated fixed commutator surface to said firstelectrical conductor distal to said proximal conductor end; and amovable electrode assembly fitted over said fixed commutator surfaceadapted to be moved proximally and distally with respect to said fixedcommutator surface and said elongated outer lead sheath, said movableelectrode assembly further comprising: an exposed, movable electrodesupported by said movable electrode assembly; means for defining amovable commutator surface within said movable electrode assemblyadapted to be moved with movement of said movable electrode assemblywhile making contact with said fixed commutator surface in a contactsegment; means for electrically connecting said exposed, movableelectrode with said movable commutator surface; and means forelectrically insulating said fixed commutator surface from exposure tobody fluids and tissue.
 2. The lead of claim 1, wherein said movableelectrode is shaped in a band surface having a predetermined band widthdefining an electrode surface area, and further comprising:means forselectively insulating a portion of said electrode surface area tothereby vary the exposed surface area or position of the electrode. 3.The lead of claim 2, wherein said selectively insulating means furthercomprises a movable, tubular insulating sheath fitted over said movableelectrode assembly and adapted to be moved proximally and distally withrespect to said movable electrode and fixed at a selected position toexpose a selected distal or proximal segment, respectively, of saidexposed, movable electrode thereby varying the exposed surface area andposition of the electrode.
 4. The lead of claim 2, wherein saidselectively insulating means further comprises a movable, tubularinsulating sheath fitted over said movable electrode assembly having awindow opening formed therein and adapted to be rotated about saidmovable electrode and be to fixed at a selected angular orientation withrespect thereto expose a selected segment of the movable electrode,thereby allowing the angular orientation of the movable electrode to beadjusted.
 5. The lead of claim 1, wherein said movable electrode isshaped in a band surface having a predetermined band width defining anelectrode surface area, and further comprising:means for selectivelyvarying said electrode exposed surface area or position.
 6. The lead ofclaim 5, wherein said selectively varying means further comprises amovable, tubular insulating sheath fitted over said movable electrodeassembly and adapted to be moved proximally and distally with respect tosaid movable electrode band surface and fixed at a selected position toexpose a selected distal or proximal band segment, respectively, of saidexposed, movable electrode thereby selectively varying said electrodesurface area and position.
 7. The lead of claim 5, wherein saidselectively insulating means further comprises a movable, tubularinsulating sheath fitted over said movable electrode assembly having awindow opening formed therein and adapted to be rotated about saidmovable electrode and be to fixed at a selected angular orientation withrespect thereto expose a selected segment of the movable electrode,thereby allowing the angular orientation of the movable electrode to beadjusted.
 8. The lead of claim 1, wherein said fixed commutator surfaceis formed of a spiral wound conductor extending along said lead body topresent a flexible conductive commutator surface.
 9. The lead of claim8, wherein said movable electrode assembly further comprises a tubularbody having proximal and distal ends and a body lumen dimensioned to fitover said elongated outer lead sheath, wherein said movable commutatorsurface is formed as a further spiral wound conductor extending withinsaid body lumen intermediate the proximal and distal ends thereof. 10.The lead of claim 1, wherein said movable electrode assembly furthercomprises a tubular body having a body lumen dimensioned to fit oversaid elongated outer lead sheath, and wherein said movable commutatorsurface is formed as a tubular, electrically conductive, surface withinsaid body lumen.
 11. The lead of claim 1, wherein said movable electrodeassembly further comprises a tubular body having a body lumendimensioned to fit over said elongated outer lead sheath and extendsproximally to said connector assembly.
 12. A method of adjusting theposition of an electrode along the length of an elongated implantablelead having a proximal lead end and a distal lead end, the lead of thetype comprising:an elongated lead body extending between said proximallead end and said distal lead end; a connector assembly located at theproximal end of said lead body; a first electrical conductor having aproximal conductor end coupled with said connector assembly andextending through a proximal portion of said lead body to a distalconductor end; and an elongated outer lead sheath extending between saidproximal and distal conductor ends for insulating said first electricalconductor through its length from body fluids and tissue; the methodfurther comprising the steps of: providing an elongated, flexible, fixedcommutator surface coupled to said first electrical conductor andextending along said lead body exposed to body fluids and tissue; movinga movable electrode assembly fitted over said fixed commutator surfaceproximally and distally with respect to said fixed commutator surface,said movable electrode assembly bearing an exposed, movable electrodesupported by said movable electrode assembly, a movable commutatorsurface within said movable electrode assembly adapted to be moved withmovement of said movable electrode assembly while maintaining contactwith said fixed commutator surface in a contact segment; and fixing saidmovable electrode assembly in the selected position and electricallyinsulating said fixed commutator surface from body fluids and tissue.13. The method of claim 12, wherein said movable electrode is shaped ina band surface having a predetermined band width defining an electrodesurface area, and further comprising the step of:selectively insulatinga portion of said electrode surface area to thereby vary the exposedsurface area or position of the electrode.
 14. The method of claim 13,wherein said selectively insulating step further comprises:fitting amovable, tubular insulating sheath over said movable electrode assembly;moving said tubular insulating sheath proximally or distally withrespect to said movable electrode to a selected position to expose aselected distal or proximal segment, respectively, of said exposed,movable electrode thereby varying the exposed surface area and positionof the electrode; and fixing said tubular insulating sheath in saidselected position to electrically insulate the un-selected proximal ordistal segment of said movable electrode from body fluids and tissues.15. The method of claim 13, wherein said selectively insulating stepfurther comprises:fitting a movable, tubular insulating sheath over saidmovable electrode assembly, said tubular insulating sheath having awindow opening formed therein; moving said tubular insulating sheathwith respect to said movable electrode to a selected position to exposea selected window of said exposed, movable electrode thereby varying theexposed surface area and position of the electrode; and fixing saidtubular insulating sheath in said selected position to electricallyinsulate the un-selected proximal or distal segment of said movableelectrode from body fluids and tissues.
 16. The method of claim 13wherein said moving step further comprises the step of:rotating saidtubular insulating sheath about said movable electrode to a selectedangular orientation of said window opening to orient said selectedwindow of said exposed, movable electrode to a desired anatomicalfeature.
 17. An elongated implantable lead having a proximal lead endand a distal lead end comprising:an elongated, tubular lead bodyextending between said proximal lead end and said distal lead end; aconnector assembly located at the proximal end of said lead body; anelectrical conductor having a proximal conductor end coupled with saidconnector assembly and extending through a proximal portion of said leadbody to a distal conductor end proximal to said distal lead end; anelongated, tubular outer lead sheath extending between said proximal anddistal conductor ends for insulating said first electrical conductorthrough its length from body fluids and tissue having an outer leadsheath diameter; an elongated inner lead sheath having a proximal sheathsection extending within said outer lead sheath between said proximalconductor end and said distal conductor end and a distal sheath sectionextending from said distal conductor end to said distal end of said leadbody; a first wire conductor wound into an elongated exposed coil oversaid inner lead sheath and extending distally of said distal conductorend providing an elongated, flexible, fixed commutator surface ofrelatively constant commutator diameter extending along said lead bodyintermediate said proximal and distal ends thereof; means for couplingsaid elongated exposed coil to said distal conductor end; and a movable,tubular electrode assembly having an outer surface and an inner surfaceof an inner diameter for making sliding contact with said outer diameterof said outer lead sheath and said commutator diameter when moved overit, said tubular electrode assembly adapted to be moved proximally anddistally with respect to said fixed commutator surface and over saidelongated outer lead sheath to a selected position, said movableelectrode assembly further comprising:an exposed electrode supported bythe outer surface of said movable electrode assembly; a second wireconductor wound into a second elongated exposed coil and positionedalong said inner surface providing an elongated, flexible, movablecommutator surface of relatively constant inner diameter for makingcontact with said fixed commutator surface in said contact segment;means for electrically connecting said exposed electrode with saidsecond wire conductor movable commutator surface; and means forelectrically insulating said coiled fixed commutator surface except forsaid contact segment.
 18. The lead of claim 17, wherein said movableelectrode assembly further comprises a tubular body having a body lumendimensioned to fit over said elongated outer lead sheath and extendsproximally to said connector assembly.
 19. The lead of claim 17, whereinsaid movable electrode is shaped in a band surface having apredetermined band width defining an electrode surface area, and furthercomprising:means for selectively insulating a portion of said electrodesurface area to thereby vary the exposed surface area or position of theelectrode.
 20. The lead of claim 19, wherein said selectively insulatingmeans further comprises a movable, tubular insulating sheath fitted oversaid movable electrode assembly and adapted to be moved proximally anddistally with respect to said movable electrode and fixed at a selectedposition to expose a selected distal or proximal segment, respectively,of said exposed, movable electrode thereby varying the exposed surfacearea and position of the electrode.
 21. The lead of claim 19, whereinsaid selectively insulating means further comprises a movable, tubularinsulating sheath fitted over said movable electrode assembly having awindow opening formed therein and adapted to be rotated about saidmovable electrode and be to fixed at a selected angular orientation withrespect thereto expose a selected segment of the movable electrode,thereby allowing the angular orientation of the movable electrode to beadjusted.
 22. The lead of claim 17, wherein said movable electrode isshaped in a band surface having a predetermined band width defining anelectrode surface area, and further comprising:means for selectivelyvarying said electrode exposed surface area or position.
 23. The lead ofclaim 22, wherein said selectively varying means further comprises amovable, tubular insulating sheath fitted over said movable electrodeassembly and adapted to be moved proximally and distally with respect tosaid movable electrode band surface and fixed at a selected position toexpose a selected distal or proximal band segment, respectively, of saidexposed, movable electrode thereby selectively varying said electrodesurface area and position.
 24. The lead of claim 22, wherein saidselectively insulating means further comprises a movable, tubularinsulating sheath fitted over said movable electrode assembly having awindow opening formed therein and adapted to be rotated about saidmovable electrode and be to fixed at a selected angular orientation withrespect thereto expose a selected segment of the movable electrode,thereby allowing the angular orientation of the movable electrode to beadjusted.
 25. The lead of claim 17, wherein said fixed commutatorsurface is formed of a spiral wound conductor extending along said leadbody to present a flexible conductive commutator surface.
 26. The leadof claim 25, wherein said movable electrode assembly further comprises atubular body having proximal and distal ends and a body lumendimensioned to fit over said elongated outer lead sheath, wherein saidmovable commutator surface is formed as a further spiral wound conductorextending within said body lumen intermediate the proximal and distalends thereof.
 27. The lead of claim 17, wherein said movable electrodeassembly further comprises a tubular body having a body lumendimensioned to fit over said elongated outer lead sheath, and whereinsaid movable commutator surface is formed as a tubular, electricallyconductive, surface within said body lumen.